Show FPDFBitmap_GetFormat() issue for bitmaps with external buffer

Add a simple test to demonstrate the problem in the bug report.

Bug: pdfium:2112
Change-Id: Iec0b62c0802fee0eb0f5e7d657b88c81cf220efa
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/115270
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/fpdfsdk/fpdf_view_embeddertest.cpp b/fpdfsdk/fpdf_view_embeddertest.cpp
index 33b8ebf..41e6ae6 100644
--- a/fpdfsdk/fpdf_view_embeddertest.cpp
+++ b/fpdfsdk/fpdf_view_embeddertest.cpp
@@ -2175,3 +2175,14 @@
 
   UnloadPage(page);
 }
+
+TEST_F(FPDFViewEmbedderTest, Bug2112) {
+  constexpr int kWidth = 595;
+  constexpr int kHeight = 842;
+  constexpr int kStride = kWidth * 3;
+  std::vector<uint8_t> vec(kStride * kHeight);
+  ScopedFPDFBitmap bitmap(FPDFBitmap_CreateEx(kWidth, kHeight, FPDFBitmap_BGR,
+                                              vec.data(), kStride));
+  // TODO(crbug.com/pdfium/2112): Should return FPDFBitmap_BGR.
+  EXPECT_EQ(FPDFBitmap_Unknown, FPDFBitmap_GetFormat(bitmap.get()));
+}